Question

Heat of neutralisation of $CsOH$ with all strong acid is $13.4Kcalmo{l}^{-1}$. The heat released on neutralisation of $CsOH$ with $HF$(weak acid) is $16.4Kcalmo{l}^{-1}$. $\Delta H^{\ominus }$ of ionisation of $HF$ is

• A. -3 Kcal
• B. -8 Kcal
• C. +3 Kcal
• D. 30 Kcal

Answer 1

The correct option is A -3 Kcal

i. $H^{\oplus }+\stackrel{\ominus }{O}H\to H_{2}O\Delta H_1=-13.4Kcal$
ii. $\stackrel{\ominus }{O}H+HF\to H_{2}O+F^{\ominus }\Delta H_2=-16.4Kcal$
iii. $HF\to H^{\oplus }+F^{\ominus }\Delta H_3=?$
$\Delta H_3=\Delta H_2-\Delta H_1$
$=-16.4-(-13.4)$
$=-3.0Kcal$